The present invention relates generally to pharmaceutical compositions and more specifically to improved protein and polypeptide pharmaceuticals for use as parenteral drugs. Recent advances in the development of genetic engineering technology have made a wide variety of biologically active polypeptides available in sufficiently large quantities for use as drugs. Polypeptides, however, can be subject to particulate formation and loss of biological activity by a variety of chemical and physical means including denaturation due to heating or freezing and by exposure to extreme pH or other chemical degradation.
Particulate formation and loss of biological activity can also occur as a result of physical agitation and interactions of polypeptide molecules in solution and at the liquid-air interfaces within storage vials. It is believed that the polypeptide molecules adsorb to an air-liquid interface, unfolding to present hydrophobic groups to air with the hydrophilic groups immersed in the aqueous phase. Once so positioned at the surface, the polypeptide molecules are susceptible to aggregation, particle formation and precipitation. It is also believed that further conformational changes can occur in polypeptides adsorbed to air-liquid and solid-liquid interfaces during compression-extension of the interfaces such as occurs from agitation during transportation or otherwise. Such agitation can cause the protein to entangle, aggregate, form particles and ultimately precipitate with other adsorbed proteins.
Particle formation due to surface denaturation can be somewhat controlled by appropriate selection of the dimensions of storage vials and by minimizing the air volume (headspace) in those vials. In this regard, partially filled containers represent the worst case for vibration induced precipitation.
Particle formation can also be controlled by incorporation of surfactants into the protein containing composition in order to lower the surface tension at the solution-air interface. Classic stabilization of pharmaceuticals by surfactants or emulsifiers has focused on the amphipathic nature of molecular groups containing both hydrophilic and hydrophobic properties within the surfactant molecule. Thus, the art teaches that one can make a stable solution of immiscible molecules such as oil-in-water or water-in-oil by selecting an appropriate surfactant as a compatibilizer. One example is the stable emulsification of soybean oil using poloxamer 188 (PLURONIC F-68, BASF Wyandotte Corp., Parsippany, N.J.). Another example is the use of polysorbate 80 (TWEEN 80, ICI Americas, Inc., Wilmington, Del.) to emulsify oil-soluble vitamins A, E and K in aqueous solution for administration via oral and vascular routes. Work by Krantz, et al., "Sugar Alcohols--XXVIII. Toxicologic, Pharmacodynamic and Clinical Observations on TWEEN 80," Bull of the School of Med., U. of Md., 36, 48 (1951) laid the groundwork leading to the listing of polysorbate 80 as a drug ingredient for which USP/NF requirements have been established in U.S. Pharmacopeia XXII.
Of interest to the present invention is the work related to use of polysorbate 80 for stabilization of antibody-based product formulations as described in Levine, et al., J. Parenteral Sci. Technol., 45, 3, 160-165 (1991). This work disclosed that the amount of surfactant required for stabilization was in excess of the theoretical minimum required to reduce surface tension. The work further showed that the need for excess surfactant beyond the theoretical minimum could be attributed to (1) the concentration required to maintain an intact protective layer on a turbulent interface during random shaking; and (2) to surfactant loosely associated with protein and bound to container walls.
Regulatory requirements limit the types and specific identities of surfactants that can be incorporated into parenteral compositions for injection into the human body. Generally accepted surfactants having a history of use and listed in the U.S. Pharmacopoeia XXI include poloxamer and polysorbate polymers. However, either of these alone may provide less than complete stabilization for the pharmaceutical compositions when used at concentrations of 0. 1% or lower. Elevated concentrations of surfactant may pose increased risk of toxic effects, earlier onset of hemolysis, and observed changes in neutrophils and platelets, both of which are involved in blood complement activation. The highest safe concentration for poloxamer 188 in approved parenteral solutions is 2.7% when it is used in limited doses as a blood substitute and is diluted as much as 10 fold in the bloodstream. Similarly, polysorbate 80, approved in parenteral solutions for over 20 years, is rarely used in concentrations greater than 0. 1% in solution volumes of 100 mL or more. Krantz et al., supra, identifies the onset of hemolysis in the dog for a polysorbate concentration of 0.1% at 90 minutes. Neonatal deaths have been associated with the use of polysorbate 80 at concentrations of greater than 1%. Accordingly, there exists a need in the art for pharmaceutical compositions providing improved protein stability which comprise only those components which are regarded as safe and are included in parenterals approved by regulatory authorities for commercial use.